Bob Ward blogged about this on the Customer Support Services blog this morning:
SQL Server Support Policy for Failover Clustering and Virtualization gets an update…
Essentially you can now run SQL Server 2005 and 2008 in a Virtualized Failover Cluster as long as the Guest OS is Windows Server 2008 or higher, the selected virtualization vendor meets the requirements for SVVP as outlined in the following article:
Support policy for Microsoft SQL Server products that are running in a hardware virtualization environment
and the Virtualization vendor meets the requirements of the following document:
The Microsoft Support Policy for Windows Server 2008 Failover Clusters.
For further information see the blog post by Bob Ward above.